Display screen portion with a transitional graphical user interface



FIG. 1 is a front view of a first image in a sequence for a display screen portion with a transitional graphical user interface; and,

FIG. 2 is a second image thereof.

The appearance of the transitional graphical user interface transitions sequentially between the images shown in the figures. This process or period in which one image transitions to another forms no part of the claimed design.

The half-tone markings in the figures indicates a contrast of one area of the claimed design from another.

The outermost broken line showing of a display screen and the other broken line showing of elements of the graphical user interface illustrate portions of the article and form no part of the claimed design. 

CLAIM The ornamental design for a display screen portion with a transitional graphical user interface, as shown and described. 